Exoplanet's atmosphere discovered

San Jose Mercury News

Published Saturday, August 08, 2009

SAN JOSE, Calif. -- HAT-P-7b is a bizarre slice of hell, a giant gas planet 40 percent larger than Jupiter that orbits so close to its sun that its year lasts just 2.2 Earth days and its atmosphere is more than 4,000 degrees Fahrenheit.

You wouldn't want to live there. But when Jon Jenkins took a deep breath at the Ames Research Center early one May morning and looked at the first scientific data flowing from NASA's newly launched Kepler spacecraft, he could hardly have been happier. The Kepler spacecraft, for which Jenkins is the lead mission analyst, had detected the atmosphere of the planet, one of several hundred known "exoplanets" that circle other stars.

The result shows that Kepler's instruments are discriminating enough to find other planets similar to Earth circling other stars, planets potentially capable of supporting life.

"I said," recalled Jenkins, a scientist with the SETI Institute, recounting his first words on the morning when he was the first to see the data -- 'I think we are looking at our first science paper."'

Consider it a scientist's version of "Hallelujah!" NASA announced the result Thursday morning, which means that the $591 million Kepler mission being managed from the NASA center at Moffett Field is poised to discover in coming years whether there are many more planets like Earth, capable of supporting life. HAT-P-7b does not.

But the detection of its atmosphere showed that more than a decade of hard work and faith for Jenkins and his fellow researchers at Ames had paid off. The method used by the Kepler spacecraft to find planets in other solar systems -- detecting minute fluctuations in light caused by a planet as it moves across the face of a distant star and then vanishes behind it -- was working.

A gas giant like HAT-P-7b is among the easiest for Kepler to track down because it is so large and because it is so close to its star, meaning its orbital period is very short and there are frequent transits across the face of its star by the planet. Detecting Earth-like planets, which orbit more distantly from their suns and therefore have much less frequent transits, will take significantly more time.

HAT-P-7b is one of about 350 known "exoplanets" orbiting other stars that have been detected by ground-based observations or spacecraft. In the first 10 days' worth of data from the Kepler following its launch in early March, scientists were able to analyze the light signatures from 52,496 stars, including one in the constellation Cygnus, 1,043 light-years from Earth, which showed distinctive drop-offs in its light emissions every two days.

"It was something that was really exciting," said Jenkins, remembering the morning of May 14, when the first scientific data was coming in from Kepler. He was the first in his office at Ames that morning.

The Ames scientists began submitting proposals for the Kepler mission in 1992, but NASA rejected their proposals four times, before finally approving one in 2001. The spacecraft was supposed to launch in 2005, but budgetary and hardware problems forced delays. A lot was riding on that first data and Jenkins was nervous.

"I came in early that morning -- I was holding my breath in anticipation," he said. "I procrastinated a little bit, and made some coffee. I fiddled around a little before I started looking through the light curves to see what we would see."

Jenkins' computer showed distinctive drops in the light coming from HAT-P-7b's star, which he excitedly showed to Bill Borucki, principal investigator for the Kepler mission, and other Kepler scientists.

Borucki "started trying to come up with arguments for how the interpretation might be wrong," Jenkins said. "One by one we knocked down all of Bill's objections."

Their findings were published in the journal Science on Thursday, an article Jenkins co-authored. The Kepler scientists believe their spacecraft should at least double the number of known planets, creating a galactic "census" that will prompt whole new theories on how solar systems form.

With the result announced Tuesday, Kepler appears ready to start tallying new planets.

"It was," Jenkins said of the realization that the probe was working, "just really amazing."